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SARS-CoV-2 infection is associated with lower blood oxygen levels, even in patients without hypoxia requiring hospitalization. This discordance illustrates the need for a more unifying explanation as to whether SARS-CoV-2 directly or indirectly affects erythropoiesis. Here, we show significantly enriched CD71+ erythroid precursors/progenitors in the blood circulation of COVID-19 patients. We found that these cells have distinctive immunosuppressive properties. In agreement, we observed a strong negative correlation between the frequency of these cells with T and B cell proportions in COVID-19 patients. The expansion of these CD71+ erythroid precursors/progenitors was negatively correlated with the hemoglobin levels. A subpopulation of abundant erythroid cells, CD45+ CD71+ cells, co-express ACE2, TMPRSS2, CD147, and CD26, and these can be infected with SARS-CoV-2. In turn, pre-treatment of erythroid cells with dexamethasone significantly diminished ACE2/TMPRSS2 expression and subsequently reduced their infectivity with SARS-CoV-2. This provides a novel insight into the impact of SARS-CoV-2 on erythropoiesis and hypoxia seen in COVID-19 patients., In this article Elahi and colleagues show that COVID-19 infection is associated with significant expansion of erythroid precursors/progenitors in the blood of patients. These cells suppress patients' immune response against SARS-CoV-2 infection. Also, they express ACE2 and TMPRSS2 and get infected with SARS-CoV-2. In turn, pre-treatment with dexamethasone significantly diminishes ACE2/TMPRSS2 expression and subsequently reduces their infectivity with SARS-CoV-2.

BackgroundT cell exhaustion compromises antitumor immunity, and a sustained elevation of co-inhibitory receptors is a hallmark of T cell exhaustion in solid tumors. Similarly, upregulation of co-inhibitory receptors has been reported in T cells in hematological cancers such as chronic lymphocytic leukemia (CLL). However, the role of CD160, a glycosylphosphatidylinositol-anchored protein, as one of these co-inhibitory receptors has been contradictory in T cell function. Therefore, we decided to elucidate how CD160 expression and/or co-expression with other co-inhibitory receptors influence T cell effector functions in patients with CLL.MethodsWe studied 56 patients with CLL and 25 age-matched and sex-matched healthy controls in this study. The expression of different co-inhibitory receptors was analyzed in T cells obtained from the peripheral blood or the bone marrow. Also, we quantified the properties of extracellular vesicles (EVs) in the plasma of patients with CLL versus healthy controls. Finally, we measured 29 different cytokines, chemokines or other biomarkers in the plasma specimens of patients with CLL and healthy controls.ResultsWe found that CD160 was the most upregulated co-inhibitory receptor in patients with CLL. Its expression was associated with an exhausted T cell phenotype. CD160+CD8+ T cells were highly antigen-experienced/effector T cells, while CD160+CD4+ T cells were more heterogeneous. In particular, we identified EVs as a source of CD160 in the plasma of patients with CLL that can be taken up by T cells. Moreover, we observed a dominantly proinflammatory cytokine profile in the plasma of patients with CLL. In particular, interleukin-16 (IL-16) was highly elevated and correlated with the advanced clinical stage (Rai). Furthermore, we observed that the incubation of T cells with IL-16 results in the upregulation of CD160.ConclusionsOur study provides a novel insight into the influence of CD160 expression/co-expression with other co-inhibitory receptors in T cell effector functions in patients with CLL. Besides, IL-16-mediated upregulation of CD160 expression in T cells highlights the importance of IL-16/CD160 as potential immunotherapy targets in patients with CLL. Therefore, our findings propose a significant role for CD160 in T cell exhaustion in patients with CLL.

Newborns are highly susceptible to infectious diseases. The underlying mechanism of neonatal infection susceptibility has generally been related to their under-developed immune system. Nevertheless, this notion has recently been challenged by the discovery of the physiological abundance of immunosuppressive erythroid precursors CD71+ erythroid cells (CECs) in newborn mice and human cord blood. Here, as proof of concept, we show that these cells are also abundant in the peripheral blood of human newborns. Although their frequency appears to be more variable compared to their counterparts in mice, they rapidly decline by 4 weeks of age. However, their proportion remains significantly higher in infants up to six months of age compared to older infants. We found CD45 expressing CECs, as erythroid progenitors, were the prominent source of reactive oxygen species (ROS) production in both humans and mice. Interestingly, a higher proportion of CD45+CECs was observed in the spleen versus bone marrow of neonatal mice, which was associated with a higher ROS production by splenic CECs compared to their siblings in the bone marrow. CECs from human newborns suppressed cytokine production by CD14 monocytes and T cells, which was partially abrogated by apocynin in vitro. Moreover, the depletion of CECs in neonatal mice increased the number of activated effector immune cells in their spleen and liver, which rendered them more resistant to Listeria monocytogenes infection. This was evident by a significant reduction in the bacteria load in the spleen, liver and brain of treated-mice compared to the control group, which enhanced their survival rate. Our finding highlights the immunoregulatory processes mediated by CECs in newborns. Thus, such tightly regulated immune system in newborns/infants may explain one potential mechanism for the asymptomatic or mild COVID-19 infection in this population.

In addition to cognitive decline, Alzheimer’s disease (AD) is also characterized by agitation and disruptions in activity and sleep. These symptoms typically occur in the evening or at night and have been referred to as ‘sundowning’. These symptoms are especially difficult for carers and there are no specific drug treatments. There is increasing evidence that these symptoms reflect an underlying pathology of circadian rhythm generation and transmission. We investigated whether a transgenic mouse model relevant to AD (APPswe/PS1dE9) exhibits circadian alterations in locomotor activity and expression of clock genes involved in the regulation of the circadian cycle. Female mice at 2 months of age were investigated in their home cage. Results show that the APPswe/PS1dE9 transgene alters levels and patterns in circadian rhythm of locomotor activity. Expression of the clock genes Per1, Per2, Cry1 and Cry2 was found to increase at night compared to day in wild-type control mice in the medulla/pons. This effect was blunted for Cry1 and Cry2 gene expression in APPswe/PS1dE9. In summary, this study suggests altered circadian regulation of locomotor activity is abnormal in female APPswe/PS1dE9 mice and that this alteration has biomolecular analogies in a widely available model of AD. Furthermore, the early age at which these effects are manifest suggests that these circadian effects may precede plaque development. The APPswe/PS1dE9 mouse genetic model may have potential to serve as a tool in understanding the neuropathology of circadian abnormalities in AD and as a model system to test novel therapeutic agents for these symptoms.